1. Field of the Invention
The present invention relates in general to engine lubrication and more particularly to a mechanism for lubricating a piston pin and a snap ring of an internal combustion engine.
2. Description of the Prior Art
Several types of piston pins for the connection between an upper end of a connecting rod and a piston are known. One usual type is exemplarily shown in FIG. 4A, in which a piston pin 10 is full floating in both a connecting rod (not shown) and a piston 12, i.e., the piston pin 10 is journalled in piston bosses 14 and an upper end of a connecting rod (not shown) provided with a bronze bushing or bearing. The piston bosses 14 are formed with snap ring grooves 16 cut in the bearing surfaces 18 thereof. Snap rings 20 are installed in the grooves 16 to prevent endwise movement of the piston pin 10. The snap rings 20 are usually formed from a cheap metal wire for the reason of economy.
In the above described type of piston, there has been no problem in lubrication of the piston pin 10 and the snap rings 20, which are lubricated by a relatively small amount of oil flowing along the piston pin 10 and supplied thereto as indicated by the arrows in FIG. 4A, in case the piston pin 10 is made of steel or the like metal.
In recent years, there has been conducted a new trial of using a piston pin made of ceramics in place of one made of steel with a view to reducing the weight, friction losses, etc. of the engine. By this trial, a problem was found in that the snap rings 20, as shown in FIG. 4B, wear excessively at the portion 20a in contact with the piston pin 10 made of ceramics, causing endwise movement of the piston pin 10 which may in turn cause excessive wear of the bearing surfaces 18 and damage of the cylinder liner.
This problem may be solved by the piston pin 10 of which end surfaces in contact with the snap rings 20 are finished highly smoothly. This, however, results in considerable cost increase. The problem may also be solved by the snap rings 20 made of a costly metal so as to have an excellent wear resistivity, but to result in considerable cost increase.